儿童是航空承运的特殊旅客，按规定，（）以下的儿童应有成人陪伴。
A.12岁
B.8岁
C.5岁
D.身高1米
参考答案：B
Annie Jump Cannon,______discovered so many stars that she was called "the census taker of the sky".
A．a leading astronomer,
B．who, as a leading astronomer,
C．was a leading astronomer,
D．a leading astronomer who
什么是双重目的抽样？
